Pretend you buy one lottery ticket per week. However, you have a choice of two types. One type tells you immediately if you have won or lost, the other does not. For either type, if you win you receive your prize the following week, and cost per ticket, probability of winning, and size of payoff are the same. There has been enough research done to predict that you will buy the ticket with immediate feedback, that is, make an observing response to obtain stimuli which signal reward and nonreward. We do not fully understand why you would make this choice, and have not determined all the variables which influence the magnitude of your preference. The objectives of the proposed research are: (1) to develop further a mathematical model which accounts for not only acquisition of the observing response, but also all the variables shown to influence its magnitude; (2) to determine additional variables which influence the observing response; and (3) to retest the effect of certain variables which have been tested in uncontrolled experimental paradigms only. The model which I have developed is based on the Rescorla-Wagner model, but assumes that both larger and smaller than expected rewards are surprising and are the basis of conditioning. It predicts acquisition of the observing response because signalled non-reward is less aversive than unsignalled nonreward. If correct, the implication is clear: transform unpredictable situations into predictable ones to reduce aversiveness of situations where nonreward or failure is unavoidable. To have control over the prior history of the organism, extraneous variables, and be able to control when large rewards are given under highly motivating conditions, a nonhuman organism which has also been shown to prefer its reward and nonreward in predictable situations will be used - the rat. Subjects will be run in an E maze apparatus and a nose-poke analog of the E maze, where in the presence of one cue, stimuli will be presented which signal reward and nonreward, in the presence of another cue, the stimuli presented are uncorrelated with reward. Speed of acquisition of the preference for the correlated condition will be measured under different levels of many independent variables.